1. Field of the Invention
The present invention relates to a film-forming device for forming a film of materials which can be formed into a film by using a vapor deposition (hereinafter, vapor deposition materials), and a light-emitting device which is typified by EL element. Especially, the present invention is effective in forming a light-emitting device by using organic materials as vapor deposition materials.
2. Description of the Related Art
In recent years, research on a light-emitting device having EL element as a self-luminous element has been activated, and specifically, a light-emitting device employing organic materials as EL materials attracts attention. This light-emitting device is also referred to as an organic EL display (OELD: Organic EL Display ) or organic light-emitting diode (OLED: Organic Light Emitting Diode).
EL element includes a layer containing an organic compound that provides an electro luminescence generated by being applied with an electric field (hereinafter, as EL layer), an anode, and a cathode. The luminescence of the organic compound includes light emission (fluorescent radiation) generated when moving back from a singlet excitation state to the normal state and light emission (phosphorescence) when moving back from a triplet excitation state to the normal state. The light-emitting device manufactured by a film-forming device and a method of forming a film according to the invention may be applied to both of the cases employing these light-emissions.
The light-emitting device is characterized by having no limitation in angle of visibility because it is a self-luminous type, which is different from the liquid crystal display device. In other words, it is superior to the liquid crystal display as a display to be used in the open air, and usages in various ways have been proposed.
EL element has such a structure that the EL layer is interposed between a pair of electrodes, and the EL layer generally has a laminated structure. Typically, such a laminated structure as “hole transport layer/light emitting layer/electron-transport layer” is employed. This structure has very high light-emitting efficiency, and most of the light-emitting devices that are currently under research and development employ this structure.
The structure laminating in order of “hole injection layer/hole transport layer/light emitting layer/electron transport layer, or hole injection layer/hole transport layer/light emitting layer/electron transport layer/electron injection layer may also be employed on the anode. It is also possible to dope the fluorescent pigment to the light-emitting layer. These layers may be formed only from low molecular materials or only from high molecular materials.
In this specification, all the layers provided between the cathode and the anode are referred to as EL layer as a generic name. Therefore, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, and electron injection layer are all included in the EL layer.
In this specification, the light-emitting element formed with the cathode, the EL layer, and the anode is referred to as the EL element, which includes a system in which the EL layer is formed between two kinds of striped electrodes arranged so as to be orthogonal with each other (simple matrix system) and a system in which the EL layer is formed between the pixel electrode and the opposite electrode connected to the TFT (Thin Film Transistor) and arranged in matrix (active matrix system).
EL materials for forming EL layer is extremely susceptible to be deteriorated; it is easily oxidized and deteriorated due to presence of oxygen or water. On that account, photolithography cannot be carried out after forming a film. In order to be patterned, the EL layer is necessary to separate a mask having an opening portion (hereinafter, a vapor deposition mask) upon forming a film. Therefore, almost sublimed organic materials are adhered to an inner wall of a film-forming chamber or an adhesion prevention shield (a protecting plate for preventing an adhesion of vapor deposition materials from an inner wall of a film-forming chamber).
In order to improve uniformity of film thickness, a conventional vapor deposition device has been grown in size since internals between a substrate and an evaporation source are widened. Further, a film-forming speed is lowered, since the internal between the substrate and an evaporation source are wide.
In addition, in the conventional vapor deposition device, a usability of high-priced EL materials is so low as 1% or less that the production cost of a light-emitting device is very expensive.
An EL material is very expensive, and the price per gram of the EL material is far higher than that of gold. The EL material is to be used as efficiently as possible. However, in the conventional evaporation device, the use efficiency of an expensive EL material remains low.